A Hot Issue

The Right Fire Extinguisher

Hib Halverson - October 11, 2012 10:00 AM


The four parts of the “fire tetrahedron” must all be present for a fire to burn.

Image: Gustavb/Wikipedia


What kind of fire is this? If you guessed Class A, you’re right. When this image was shot, the vast majority of what’s burning is rubber and plastic, but for this fire, forget a fire extinguisher. The Slackwood Fire Company extinguished this vehicle fire in Trenton, New Jersey in August 2011. In this particular incident a passing motorist attempted to attack the fire with a portable extinguisher, but retreated because the fire was too large.

Image: Michael Radcliffe/


This yellow powder is ABC dry chemical, the most common fire suppression agent for use in portable extinguishers.


These two Kidde extinguishers carry the same rating, 1-A:10-B:C. The unit at left is charged with “Halation” and the unit at right is charged with ABC Dry Chem. As you can see, it takes a much bigger extinguisher to put out a fire if you’re using HFC gas.

Image: Kidde Residential and Commercial


These two Kidde extinguishers are about the same size and weight but have different ratings, different hardware and different prices. At left is a Kidde Pro Series model 460, rated 4-A:60-B:C. The unit on the right is a Kidde Pro-Plus model 10MP, rated 4-A:80-B:C. The higher rating is because of its higher charge pressure. The 10MP also has a more robust handle assembly, hose and nozzle.


Many public and private entities offer fire extinguisher training. In 2011, the Central Columbia School District in Pennsylvania hosted “Fire Safety Days” during which the Espy Fire Company offered students training on proper fire extinguisher use.

Image: Central Columbia School District


We can’t emphasize enough the importance of first calling 9-1-1 when there’s a fire, then trying to use a portable extinguisher ONLY if the fire is small and you have an escape route. If the fire is spreading fast or you don’t see an escape route, you don’t need a fire extinguisher – you need a fire truck, like Santa Barbara County California’s Paramedic Engine 11.


Nargan Fire and Safety’s Eric Persson tells us that portable fire extinguishers should be inspected annually and serviced immediately after use or whenever the extinguisher’s gauge is in the red “recharge” range.


Fire extinguishers are regulated primarily by State Fire Marshals, and usually each requires a tag to display the extinguisher’s service history.


Extinguisher mounting requires some thought. You want the unit where it can be deployed easily, but not mounted in a way which interferes with the vehicle occupants or presents a safety hazard. The owner of this Chevy S10 Blazer mounted a Kidde ProPlus 5MP, 3-A:40-B:C fire bottle (PN 4680010) on the side of the transmission tunnel. It’s away from the passenger’s legs, but easily accessible by driver or passenger.


The owner of this ’71 Corvette used the biggest Ansul extinguisher, a Sentry A05, rated 3-A:10-B:C (p/n 429001), he could fit in the available space and mounted it in a custom-built aluminum bracket under the passengers legs, just ahead of the passenger seat.


This Kidde ProPlus 10MP 4-A:80-B:C extinguisher (p/n 468002) is mounted on the wall in a two-car garage. For extinguishers hanging on walls, fire safety experts say the mount or hanger should be installed such that the top of the extinguisher is between 3½ and 5 feet above the floor.

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The National Fire Protection Association (NFPA) tells us that, in 2010, the last year statistics are available, there were 215,500 vehicle fires in the U.S. – one every 146 seconds. Those fires killed 310 people, injured 1,590 and did $1.4 billion worth of damage.

Some believe vehicle fires are caused mainly by gasoline or other flammable liquids. According to a June 2010 NFPA study of “U.S. Vehicle Fire Trends and Patterns,” during a four-year period, 2003-2007, only two percent of vehicle fires started in the fuel system. Another three percent were caused by collisions or rollovers. The study reveals that nearly 75 percent of the fires were caused by mechanical failures or electrical problems and two-thirds of them began in the engine, drivetrain, or wheel areas. Those fires resulted in 35 percent of the deaths, 46 percent of the injuries, and 53 percent of the property damage.

Confronted with fire in your car, garage or workshop, do you know what to do, first? Do you have a fire extinguisher? Do you know what kind of fires it can put out? Lastly, do you know how to use that extinguisher? NFPA tells us that a third of vehicle fire injuries were to people who tried to fight the fire themselves. Clearly, folks who do carry fire extinguishers need to be better educated about putting out fires.


The Fours of Fire

Just what is “fire,” anyway? It’s rapid oxidation of a combustible material releasing heat, light, and reaction products such as smoke, sparks or embers. A fire has four components, an idea illustrated by the “fire tetrahedron.” The four parts are: heat, oxygen, fuel and a chemical chain reaction. Eliminate one or more of those four and there’s no fire. If you cool the fuel below its ignition temperature, take away the oxygen, remove the fuel or interfere with the chain reaction; the fire goes out.

Fires are categorized into five classes and four of them may occur in vehicles or garages.

Class A fires are fueled by wood, paper, plastic, rubber, cloth, upholstery and similar materials.

Class B fires are fueled by flammable liquids or gases.

Class C fires are fueled by or burn on or in electrical equipment which is energized or “live”. A Class C fire will be a Class A fire or, occasionally, a Class B fire, with what’s burning, also, being electrically charged.

Class D fires are fueled by combustible metals.

One example is magnesium, used in road wheels along with chassis parts and, occasionally, in underbody structures. Complete masses of combustible metal are usually not significant fire risks because they conduct heat away from hot spots so well that combustion is not sustainable, i.e., it requires a lot of heat to set a mag wheel on fire. Metal fire risks are far greater when machine shavings and other fine metal powder or debris are present. For example: aluminum powder is highly flammable – that’s why it’s sometimes called “flash” powder.


Extinguishers and Their Agents

Portable fire extinguishers small enough to be carried in your car, or somewhat larger units to hang on the wall in your garage, are designed to put out a fire in its early stages – typically the first two minutes – before it grows such that significant damage to the vehicle or home or injury to the occupants takes place. Once the fire is larger than that, forget hand extinguishers. Run the other way to a safe location then dial 9-1-1 because you need a fire truck – not a fire extinguisher.

Portable extinguishers are often the “stored pressure” type, meaning they are filled with a fire suppression or extinguishing agent and then pressurized, usually with either nitrogen gas, carbon dioxide or air. They are metal cylinders, either steel or aluminum, topped with a handle and a lever. A pressure gauge mounted on the handle assembly tells the user if the extinguisher is fully charged. A ring pin locks the lever and handle and must be removed or “pulled” before the extinguisher can be used.

Portable fire extinguishers use a variety of extinguishing agents: water, carbon dioxide (CO2), dry chemical powders and so-called “clean agents”. These fire suppression agents are rated by the class or classes of fire for which they are effective. Water is great as long as you are fighting a Class A fire. Don’t use water for a Class B, C or D . It may spread a Class B fire. You can be shocked or electrocuted if you use it on a Class C fire. Spray water on a Class D fire and an explosion will result.

CO2 shouldn’t be used on a Class A fire because it may spread rather than suppress it. Even if it won’t spread the fire, CO2 is not very effective on a Class A fire, because it may not displace enough oxygen to extinguish the fire. CO2 can be effective on B and C fires and is one of the agents recommended for fire suppression in places where the extinguishing agent residue can cause problems after the fire is out.

Dry chemical agents are widely used in fire extinguishers carried in vehicles or intended for initial fire suppression in garages or work areas. Three types of dry chemical powders are common.

ABC-rated, “multi-purpose dry chemical” fire suppression agent (some call it “ABC dry chem”) is mono-ammonium phosphate powder and is often used in stored pressure extinguishers. When sprayed on a Class A fire, at 350°F, it melts, then coats the fuel, making a barrier between it and oxygen. It breaks the chain reaction in a Class B fire. It is, also, a Class C extinguishing agent meaning it will not conduct electricity, so current will not flow from the burning electrical components, up the stream of extinguishing agent, through the metal of the extinguisher and into your body. If moisture is present, ABC dry chem is mildly corrosive so the contacted area should be cleaned once the fire is out. Fire extinguishers charged with ABC dry chem are the best choice for fighting vehicle or small garage fires.

Another common fire suppression agent is “regular dry chemical”, which is ordinary sodium bicarbonate – baking soda. It was the first dry chemical extinguishing agent developed and is often used in lower cost extinguishers. Sodium bicarbonate is B:C-rated but is not as effective as ABC dry chem and is not effective on Class A fires.

A third type of dry chemical agent with which car enthusiasts might come in contact, though not often because of its cost, is potassium carbonate, commonly known as “Purple-K”. It’s Class B:C-rated and is common in military, industrial or commercial environments where gasoline, solvents, oil or flammable gases are processed, handled or stored. Purple-K is the dry chemical agent of choice for the oil and gas industry and the only dry chemical agent approved for aircraft fires. Of all common fire suppression agents covered here, it’s the most effective at suppressing Class B fires.

Some automotive extinguishers use hydroflurocarbon (HFC) gases, also called “clean agents,” such as Kidde “Halotron”, Ansul “FE-36 CLEANGUARD,” HFC-227ea and others. HFCs work by one or a combination of: displacing oxygen, removing heat from the combustion zone or inhibiting the chemical chain reaction. The attraction of HFCs are, when the fire extinguisher is discharged, there is no cloud of yellow, white or purple powder and there is no corrosive residue to clean up after the fire is out – which you might think is a good thing if the fire is under the hood of your pristine ’69 Camaro. The downsides of HFC agents are: 1) high cost, both initial purchase and refilling, and 2) for a given fire extinguisher size, it puts out less fire than dry chemical fire extinguishers.

Our view is that if your car is on fire, first priority is to make sure you and your passengers are safe and the second priority is to get the fire out and, for a given extinguisher size, ABC dry chemical can put out a much larger fire or can be discharged for a longer period than an extinguisher using an HFC agent. For carrying in the car, we’ll take ABC dry chem and a clean up job versus HFC and, perhaps, an ineffective fire suppression attempt.

Class D fire extinguishers are uncommon in the automotive enthusiast community because of the rarity of metal fires and the cost of the extinguisher, but if you regularly do metal finishing work on aluminum parts and generate a lot of filings, powder or dust, you should consider one. Class D extinguishers for aluminum fires use sodium chloride – salt crystals – as an extinguishing agent.


Rating Numbers

While all extinguishers are rated for the fire class for which they are effective, Class A and B units are also rated as to the size of fire they can extinguish and, for Class B extinguishers, for how long they can be discharged. The testing and rating of fire extinguishers is done by Underwriters Laboratories and the procedure is complicated. We should add that one should never use a fire extinguisher for vehicle or workshop protection which is not UL-rated.

If the extinguisher carries an “A” rating, such as “1-A:10-B:C,” the number before the “A” designates the size of a burning crib of wood which can be extinguished by an experienced user. A rating of 1-A means that extinguisher can put out a burning, 20x20x24-inch crib of 2x2-inch boards (9,600, stacked in 12 layers of six pieces. A 2-A extinguisher can put out a 20,000 cubic inch crib (25x25x32-inch of 2x2s) and each jump in a rating number doubles the volume of the crib it can extinguish.

With Class B extinguishers, the numeric rating is 40 percent of the area of a four-inch deep pan of burning heptane, a flammable solvent which is a minor component of gasoline. If an Underwriters Laboratories fire fighter – the “UL expert” – can put out a 25 square foot pan of heptane with a given fire extinguisher, its rating is 10-B. If it’s capable of putting out a fire twice that size, its rating is 20-B and so on.

It is important to remember that the numeric rating on a Class A or B extinguisher is merely a guideline one can use to compare extinguishers. It does not accurately quantify how large a fire the average user can put out because, with a given fire extinguisher size, a UL expert in a laboratory testing environment is going to be able to extinguish a bigger fire than can an inexperienced user in a real world situation. Also atmospheric conditions, fire location, and fuel type will affect the fire suppression effort such that the extinguisher in question may have an effect in the “real world” quite different from what happened during the rating process.


How to Use a Fire Extinguisher

If you retain only one idea from this article, remember: “PASS,” an acronym which might save your car, your house – or your life. That’s P for: pull the ring pin, A for: aim at the base of the flames, S for: squeeze the handles together and S for: sweep the nozzle from one side of the fire to the other.

Confronted with a fire, first, make the fight-or-flight decision. In your determination to either try and put out the fire or stand back and wait for a fire truck, consider the type and size of the fire, the rating of your extinguisher, your experience and your intestinal fortitude.

Let’s say a fuel hose broke, gas pooled on top of your engine then dripped onto the headers and ... poof! The engine bay is going up and the flames are four feet high. You have a little 2-B:C-rated fire extinguisher you bought at a convenience store. Run the other way and call 9-1-1. Tell the dispatcher your location and that there’s a vehicle fire with the engine fully involved, then wait for the firemen.

On the other hand, if you are confident of your abilities, the wind is not blowing too hard and you’re armed with a 1-A:10-B:C fire bottle, you stand a good chance of getting the fire out.

Make sure you have a clear escape route in case the fire gets too large – best is to have that escape route at your back. If you have to run a distance to the fire and your extinguisher is a larger unit, carry it cradled in your arms like a baby. Deploy your fire extinguisher by holding the handles in your right hand and have the fingers on your left hand on the ring pin. Then, approach the fire from upwind, to distance of six to 10 feet, and – PASS. Pull the pin then, aim at the base of the flames, squeeze the handles and sweep the discharge nozzle from side-to-side.

If the fire is under the hood and the hood is closed, don’t open it! The blast of fresh air often will cause the fire to flare up in your face. Approach the front of the car, get down low and attempt to spray the powder under the front end and up into the engine bay. Another firefighter’s trick for a “closed-hood fire” is to point the nozzle at the ground under the engine and behind a front tire then try and “bounce” the spray off the ground and into the space under the hood. As soon as the fire is out, wash down the burned area with water to cool any remaining fuel and wash away the dry chemical agent.

How about a fire in your garage or shop? Say you’re using a cutting wheel to shorten some tubing you have chucked in a vise and you don’t see sparks flying into the trash can behind you. The day before, you filled the can with some oily rags and paper scraps. Suddenly, you smell smoke and turn around to find the trash can is a raging inferno and your favorite Kyle Busch wall poster starting to burn.

First, make sure you have an escape route in case the fire gets too big, then grab that 3-A:40-B:C extinguisher you’ve kept hanging next to your bench. Pull the pin, aim at the trash can, then squeeze the handles and, in this case, sweep side-to-side along with up and down, so you get the burning wall poster as well as the trash can.

Want more information? You can find videos of how to use fire extinguishers on YouTube. Also, some local fire departments offer fire extinguisher training. Lastly, employers, as a function of their company’s safety program, may offer fire extinguisher training.



For this article, we had Nargan Fire and Safety, a fire extinguisher service in the south end of California’s Central Coast, service two extinguishers for us. In business since 1964, Nargan has mobile units and the representative who responded to our west coast office was Eric Persson, one of Nargan’s licensed fire suppression equipment service technicians.

Persson has a decade of experience working with fire extinguishers. He told us that Nargan is an Amerex Corporation dealer and that they prefer Amerex extinguishers because of their quality, durability and ease of service. Persson also suggested Tyco’s “Ansul” brand as another good choice. He added that some extinguishers, popular with consumers because of low prices, are not as durable and more difficult to service than Ansul and Amerex units. Persson added that some extinguishers are made offshore and some of those have proven deficient in quality.

Some of the Kidde extinguishers we evaluated for this story had “Made in Mexico” printed on their cylinders. Upon removing one of the Mexican-sourced units from factory packaging, we found it discharged. We had Nargan recharge it and during its disassembly, Eric Persson showed us where the ABC dry chem had caked around the top of the cylinder and told us that meant moisture was in the extinguishing agent. Moistened fire suppression agent is a quality problem, which can cause extinguisher failure. Persson identified a second problem with the same unit: the valve seat inside the handle assembly was square rather than machined at an angle to match the conical rubber seal on the valve. It was unknown whether that was a manufacturing defect or a deficient design, but either way, the sharp edge will likely compromise the life of the seal. Persson said that that moisture compromising extinguisher reliability and parts quality issues are problems with foreign-made extinguishers to the point that Nargan Fire and Safety prefers not to sell those particular brands.

The other extinguisher we had Nargan Fire and Safety recharge was an older Pittway “First Alert” 2-A:10-B:C unit. It had no moisture in it and a beveled valve seat in the handle assembly. After recharging, that unit was returned to service in our shop.

At the end our extinguisher recharge session, Persson reviewed a few maintenance basics with us. He said a fire extinguisher’s pressure gauge should be checked every month. If the needle is in the red zone, the extinguisher must be recharged by a licensed service vendor. If you discharge an extinguisher, have it recharged as soon as possible. Persson explained that fire extinguishers which are not used should be inspected annually by a licensed fire extinguisher service vendor. Extinguisher cylinders must be hydrostatically tested every 12 years. No licensed fire extinguisher service vendor will refill an extinguisher with an out-of-date cylinder. To “hydrostatic” a fire extinguisher cylinder is expensive, so with some low cost units sold to consumers, it’s less costly to simply replace them.

The best choice in portable fire extinguishers for auto enthusiasts? We think an extinguisher, charged with ABC dry chemical suppression agent and rated 1-A:10-B:C is a good choice but a 2-A:20-B:C unit is much better if you have the space for it. If you insist on an extinguisher charged with a clean agent, get the biggest one which can fit your mounting location.

A fire extinguisher needs to be mounted securely and safely in the vehicle. Many units designed for carrying in a car come with some type of mounting bracket or cradle. If your extinguisher does come with a mount, we strongly suggest using it because the unit’s maker has designed the mount specifically for that extinguisher. Locate the extinguisher in a place where it can be easily reached, but does not pose a hazard in a collision. One place you absolutely do not want to mount a fire extinguisher is on the windshield post inside the car. In a frontal impact, your head or your passenger’s head could hit the fire extinguisher, resulting in severe head injury or death.

For your garage or shop, have at least a 3-A:40-B:C-rated unit or, better yet, a 4-A:60- or 80-B:C, filled with ABC dry chem. Again, if your workshop activity involves a lot of metal finishing work on aluminum parts, consider a Class-D extinguisher.


The Bottom Line

We can’t emphasize enough that portable fire extinguishers are for attacking a fire before it gets too large and/or is spreading fast. If a fire is already that way when you become aware of it, don’t bother with a fire extinguisher. Run the other way and dial 9-1-1 because you need a big truck with flashing lights, siren, big hoses and a company of firefighters. Another issue we can’t repeat too many times: if you decide to fight a fire with a portable extinguisher, make sure you have an escape route, approach to six to 10 feet then PASS.

Thanks to the people at Tyco International’s Ansul brand, UTC Fire and Security’s Kidde brand, John Dregenburg, Consumer Safety Director at Underwriters Laboratories and Nargan Fire and Safety for assistance in researching this article.